"Never have experiments been conducted with greater care, caution, and exactitude than those of Stas. It is said that the greatest variation between his many individual determinations of the atomic weight of the same element was from .005 to .01. ...Some illustrations may be given of his care in purifying materials. He purified iodine either (1) by dissolving it to saturation in an aqueous solution of potassium iodide, precipitating it with an excess of water, rather less than was sufficient to throw down the full amount possible, washing, distilling with steam, and drying under a bell-glass beside calcium nitrate (the only salt which was found not to affect the purity of iodine); or (2) by acting with solution of ammonia on the iodine to be treated, thus forming nitrogen iodide, or diodamine, as he considered it, decomposing the violently explosive body by heating with excess of water to 60° or 65° Centigrade, and distilling and drying as before. By this latter method he treated some 10 kilogrammes of iodine in lots of 500 grains at a time."